One pressing need for better soil classification techniques than have been available before, is the need to locate contaminating petroleum products, hazardous waste materials, and the like. For example, at refineries and old filling station sites, petroleum products such as crude oil and gasoline have sometimes been spilled or have leaked onto the soil and have seeped downwardly through the soil. It is of great assistance in cleaning up such contamination to know exactly where this material is principally concentrated, and the present invention makes this possible. The concentration may be anywhere from just below the ground surface down to one hundred feet or more below ground, and the present invention makes it possible to detect the location of such a concentration. The invention therefore makes it that much easier to remove the contaminated layer of soil. This will be explained further and in detail below.
This is only one example of the many instances in which it is important to know the characteristics of soil. For example, another example is the desirability of detecting below-ground (or on level ground) ice and its state of complete solidity or partial melting.
Two types of soils are recognized as basic: non-clay minerals, typified by sands, and clay minerals, typified by clays.
Present methods of classification of soil between clays and sands have been based on an arbitrary line of demarcation at a particle size of 2 microns (0.002 mm); smaller-particle soils have been treated as clay, and larger-particle soils have been treated as sand. However, this arbitrary boundary does not always correspond with the plasticity of such soil. It is possible for soils to exhibit the plasticity characteristics of clay in the presence of water, both above and below the 2 micron level of particle size, and it is also possible for soils to be properly classified as non-clay minerals above and below that level.
The present invention provides a quantitative and fundamental demarcation between clays and sands, by using the dielectric dispersion characteristics of the soils to indicate whether the soil is really a clay or a sand.
It is also important to quantify the intercluster and intracluster natures of soils and the void ratios shown by such clusters in cohesive soils or clays.
Other soil characteristics mentioned below, are also extremely desirable to determine.
One trouble with prior art methods of determinating soil characteristics was the amount of time those methods required. First, the soil layer had to be uncovered or drilled into. Then a sample was taken. Then that sample was taken away and subjected to laboratory apparatus, usually remote from the original site. In situ equipment was sometimes used, but with varying degrees of success; indeed, in situ methods were limited largely to determining only a few of the characteristics needed.
Several different in situ testing techniques are in current use for evaluation of the soil properties that establish one or more empirical criteria for the prediction of the potential behavior of soils. The standard penetration test and the cone penetration test are widely used and are very useful; others include pressure meter tests and bore hole shear tests; also, dilatometers are being used on a moderate scale. However, the reliability and usefulness of the test results obtained from these various techniques are limited because of several reasons. The drainage conditions in the soils during the in situ testing may be unknown. The failure modes may not simulate those anticipated for the actual product, and in some cases the exact failure mode is unknown. Due to the unknown drainage and failure conditions and the specific nature of the testing procedures and the failure mode simulated in different techniques, the interpretation of the test results has been highly empirical. For the same reason generalization of the test results has been very difficult.
The present invention makes it possible to investigate soils in situ and to do so very quickly. For instance, some determinations that formerly took a day to determine once the soil was reached, can now be done in less than five minutes by employing the present invention.
The present invention has both method and apparatus aspects. Its apparatus aspects provide a system by which the needed measurements can be taken, and the method includes not only the method of taking these measurements, but also methods of using them to determine the characteristics of the soil.